1. Field of Invention
The present invention relates to a magnetoresistive effect element (MR element) in a CPP-type structure that detects magnetic field intensity as a signal from a magnetic recording medium, and so on, a thin film magnetic head with the MR element, and a head gimbal assembly and a magnetic disk device that have the thin film magnetic head.
2. Description of Related Art
In recent years, with an increase in the high recording density of a magnetic disk drive (HDD), there have been growing demands for improvements in the performance of a thin film magnetic head. For a thin film magnetic head, a composite type thin film magnetic head has been widely used; it has a structure where a reproducing head having a read-only magnetoresistive effect element (hereinafter, magneto-resistive (MR) element), and a writing head having a write-only induction type magnetic conversion element are laminated together.
Generally, a shield layer is formed in a reproducing head to restrict an area of a medium that interferes with a reproducing element. Currently, in a conventional mainstream head structure, a first shield layer, a second shield layer and an MR element are connected in series without an intershield insulating layer. This structure is referred to as an MR element in a current perpendicular to plane type (CPP-type) structure. In consideration of the efficiency of heat radiation and maintenance of an output, and so on, a CPP-type structure is an essential technology to realize a high recording density of 500 Gbits/in2 or more.
A general CPP-type element with a spin valve is briefly explained below. A typical spin valve CPP-type element is formed by a lamination structure for its main layers as follows: a lower electrode layer/an under layer/an antiferromagnetic layer/a ferromagnetic layer (1)/a spacer layer/a ferromagnetic layer (2)/a cap layer/an upper electrode layer. The top most layer is the upper electrode layer, and the bottom most layer is the lower electrode layer. In the specification, a lamination layer may be described as having the above format.
A magnetization direction of the ferromagnetic layer (1), which is one of the ferromagnetic layers, is pinned in the perpendicular direction to a magnetization direction of the ferromagnetic layer (2) when the externally applied magnetic field is zero. The ferromagnetic layer (2) is generally referred to as a magnetic free layer. The magnetization direction of the ferromagnetic layer (1) can be pinned by making an antiferromagnetic layer adjacent thereto and providing unidirectional anisotropic energy (also referred to as “exchange bias” or “coupling magnetic field”) to the ferromagnetic layer (1) by means of exchange-coupling between the antiferromagnetic layer and the ferromagnetic layer (1). For this reason, the ferromagnetic layer (1) is also referred to as a magnetic pinned layer.
As mentioned above, a CPP-type element that is configured with a connection between a shield layer and an MR element through a metal is advantageous because it increases heat radiation efficiency and operating electric current. In this element, a smaller cross sectional area of an element has a larger resistance value and a larger resistance variation. Namely, it is an appropriate structure for a, so called, narrower track that narrows a track width. A narrower track width increases a track per inch (TPI), and it is an essential technology for increasing the recording density of an HDD.
However, in view of the high frequency characteristic of the above element, an extreme increase in the resistance of such an element is unfavorable. In other words, with the recent increase in the recording density, it is necessary to improve the high frequency characteristic of a reproducing signal. In order to improve the high frequency characteristic of a reproducing signal, it is important to match the following factors: an impedance of an MR element part; an impedance of an amplifier; and an impedance of a transmission line connecting the MR element part; and the amplifier. Since these impedance values are restricted by an impedance of a transmission line, an MR element needs to have a lower resistance value to improve the high frequency characteristic. Therefore, research and development has been conducted for a CPP-GMR element that has a spacer layer made of a low resistance material instead of having a TMR element with a tunnel barrier that has a high resistance value.
With consideration of the situation described above, the present invention is provided. An object of the present invention is to provide an MR element having a large magnetoresistive variation in a lower resistance area that has a resistance value of 0.3 Ωμm2 or smaller with respect to its area resistivity (AR), a thin film magnetic head that has the MR element mentioned above, and a head gimbal assembly and a magnetic disk device that have the thin film magnetic head mentioned above.
As related art that may be related to the present invention and that discloses a method to increase an MR ratio of a CPP-GMR element, the following four references are given by an example.
(1) Japanese laid-open patent publication No. 2008-34523 discloses that, in a current confined path (CCP)—current perpendicular to plane (CPP) type giant magnetoresistive effect element (GMR) having a magnetic pinned layer, an intermediate layer, and a magnetic free layer, the GMR element is configured with the intermediate layer that is made of single crystalline or polycrystalline magnesium oxide (MgO) with a layer thickness of 1 nm or lower. The intermediate layer is preferentially oriented with a (001) crystal plane and a BCC-CoFe (001) structure is formed over the intermediate layer.
However, the magnesium oxide (MgO) of the intermediate layer is not an intended material of the present invention and is not an appropriate material for decreasing resistance.
(2) Japanese laid-open patent publication No. 2008-4956 proposes that, in an MR element with a magnetic tunnel junction structure that includes a first ferromagnetic material with a BCC structure formed on a first plane of a tunnel barrier layer and a second ferromagnetic material with a BCC structure formed on a second plane of the tunnel barrier layer, the MR element is configured with the tunnel barrier layer made of either single crystalline MgO (001) or polycrystalline MgO in which a (001) crystal plane is priority oriented, the first ferromagnetic material made of either Fe (001) or an Fe alloy system (001), and the second ferromagnetic material made of either Fe (001) or an Fe alloy system (001).
However, the magnesium oxide (MgO) of the tunnel barrier layer is not an intended material of the present invention and is not an appropriate material for decreasing resistance.
(3) Japanese laid-open patent publication No. 2008-235528 proposes that an MR element is configured with the following layers in a bottom up direction; an under layer that is made of NiFeN and is formed on a main surface of a substrate, a pinning layer that is made of an antiferromagnetic material containing Ir and Mn and is formed on the under layer, a reference layer that is made of a ferromagnetic material in which a magnetization direction is pinned by exchange-coupling with the pinning layer directly or indirectly through another ferromagnetic layer and is formed on the pinning layer, a nonmagnetic layer that is made of a nonmagnetic material and is formed on the reference layer, and a free layer that is made of a ferromagnetic material in which a magnetization direction varies depending on the externally applied magnetic field and is formed on the nonmagnetic layer.
However, this reference does not disclose or suggest a combination of an under layer made of NiFeN and a CoFe layer made on the under layer. The nonmagnetic layer is made of MgO. The magnesium oxide (MgO) of the nonmagnetic layer is not an intended material of the present invention and is not an appropriate material for decreasing resistance.
(4) Japanese laid-open patent publication No. H06-195645 discloses a magnetoresistive effect type head configured with a magnetoresistive effect film that is made of a NiFe alloy, a magnetic material with magnetoresistive effect, and a magnetic sensitive part made of a NiFe alloy in which a plane direction is oriented as a (100) orientation with respect to a layer surface of the magnetoresistive effect film.
However, this reference is related to a magnetic layer made of a NiFe alloy. This reference does not disclose or suggest a combination of CoFe in a (001) orientation and Cu in a (001) orientation.